A bearing is typically selected on the basis of its load rating relative to the applied loads and the requirements regarding bearing life and reliability. Values for the basic dynamic load rating C and the basic static load rating C0 are listed in the product tables.
Both dynamic and static bearing load conditions should be independently verified and should include any heavy, short duration shock loads that may occur on rare occasions.
Dynamic load ratings
The basic dynamic load rating C is used for life calculations involving dynamically stressed bearings, i.e. bearings that rotate under load. It expresses the bearing load that will result in an ISO 281:2007 basic rating life of 1 000 000 revolutions. It is assumed that the load is constant in magnitude and direction and is radial for radial bearings and axial, acting centrically, for thrust bearings.
The basic dynamic load ratings for SKF bearings are determined in accordance with the procedures outlined in ISO 281:2007. The load ratings provided in this catalogue apply to chromium steel bearings, heat-treated to a minimum hardness of 58 HRC, and operating under normal conditions. An exception to this are polymer bearings.
SKF Explorer performance class bearings have undergone, among other things, material and manufacturing improvements that require adjusted factors to calculate the dynamic load ratings in accordance with ISO 281:2007.
Static load ratings
The basic static load rating as defined in ISO 76:2006 corresponds to a calculated contact stress at the centre of the most heavily loaded rolling element / raceway contact. The contact stress values are:
- 4 600 MPa for self-aligning ball bearings
- 4 200 MPa for all other ball bearings
- 4 000 MPa for all roller bearings
This stress produces a total permanent deformation of the rolling element and raceway, which is approximately 0,0001 of the rolling element diameter. The loads are purely radial for radial bearings and axial, centrically acting, for thrust bearings.
The basic static load rating C0 is used under the following conditions:
- very low rotational speeds (n < 10 r/min)
- very slow oscillating movements
- stationary bearings under load for extended periods
Verification of static bearing loads is performed by checking the static safety factor of the application, which is defined as
|s0||=||static safety factor|
|C0||=||basic static load rating [kN]|
|P0||=||equivalent static bearing load [kN]|
The maximum load that can occur on a bearing should be used when calculating the equivalent static bearing load. For additional information about the recommended values for the safety factor and its calculation, refer to Selecting bearing size using static load carrying capacity.